1. Field of the Invention
The present invention relates to an apatite composite ceramic which is a useful material especially for artificial dental root, artificial bone and the like.
2. Description of the Prior Art
In recent years intensive studies have been made on implants such as artificial dental root and artificial bone. Substantial efforts have been made to search for those materials which enable provision of such implants with not only good biological affinity (referred to as affinity to live bone hereinafter) but also high mechanical strength and, consequently, a long effective life.
A representative known material for implantation is sintered-apatite. As the starting material of the sintered-apatite there is used a synthetic hydroxyapatite the composition of which is essentially the same as the main inorganic component of bone. The sintered-apatite obtained from the synthetic hydroxyapatite is, therefore, excellent in biological affinity.
On the other hand, when the sintered-apatite is to be used as implant material, the sintering must be carried out at a temperature as high as possible, for instance, at 1400.degree. C. in order to obtain the necessary high mechanical strength. However, it has been known to those skilled in the art that the biological affinity is reduced when the sintering is carried out at such high temperature. This is because, during the sintering, there occurs a change of chemical structure from hydroxyapatite to oxyapatite with elimination of the hydroxy group. In this connection it has been reported that in order to obtain high biological affinity it is desirable to carry out the sintering at a temperature lower than 1100.degree. C., in particular, in the range of 700.degree. to 900.degree. C.
Many attempts have already been made to find means for improving the mechanical strength of sintered-apatite while avoiding the use of such high sintering temperature adverse to the biological affinity. As a solution to the problem it has been proposed to add to the synthetic hydroxyapatite powder some particular additives such as CaO, MgO, Al.sub.2 O.sub.3 and other reinforcing materials aiming at improvement of mechanical strength and also achievement of lower sintering temperature (cf. Japanese Patent Application Publication No. 40,776/1982).
Obviously, the solution as mentioned above is not satisfactory and cannot solve the problem completely. The additives and reinforcing agents themselves have no biological affinity. If such materials are added to the synthetic hydroxyapatite powder, the sintered-apatite obtained from the mixture will exhibit biological affinity degraded by the additives.
Because of the difficulties mentioned above, there has not yet been provided any sintered-apatite which satisfies the requirements of good biological affinity and high mechanical strength at the same time.